The prior art of hammer-drills has been very highly developed over the years. These tools usually have a floating rotary-reciprocatory output spindle journaled in the housing for driving a suitable tool bit coupled thereto. In operation, the spindle is retracted axially within the housing and against the force of a suitable resilient means, upon engagement of the tool bit with the work and a manual bias force exerted by the operator on the tool. A fixed hammer member is secured in the housing, and a movable hammer member is carried by the spindle. The movable hammer member has a ratcheting engagement with the fixed hammer member to impart a series of vibratory impacts to the spindle in the hammer-drilling mode of operation. A shiftable means acts upon the spindle to change from the "drilling" mode to the "hammer-drilling" mode, and vice versa. In the drilling mode, the shiftable means moves the spindle forwardly in the housing by a sufficient amount, such that upon the subsequent retraction of the spindle within the housing (due to engagement of the tool bit with the work and the manual bias force exerted by the operator on the tool) the cooperating hammer members are spaced too far apart and hence do not engage each other. In the hammer-drilling mode, however, the spacing between the ratcheting teeth is reduced, and the cooperating hammer members impart their vibratory impacts to the spindle. Additionally, the art has disclosed various configurations of a two-speed or multi-speed transmission for use with hammer-drills. The cooperating hammer members, the shiftable means, and the multi-speed transmission thus constitute three essential mechanisms of a multi-speed hammer-drill.
In the prior art, of which I am aware, these three mechanisms of a multi-speed hammer-drill have been mounted at various locations within the tool housing; and not all have been centered coaxially about the output spindle or directly adjacent thereto. As a result, the multi-speed hammer-drills of the prior art have been unduly complicated, hence somewhat expensive, as well as cumbersome and awkward to use.